The present invention relates to a method and apparatus for the prevention of the attachment of foreign bodies to parts of a connecting rod linkage for the adjustment of the blades of a controllable pitch propeller in a motor-driven watercraft. In watercraft, connecting rods of a connecting rod linkage are adjustable by means of an adjusting linkage via a rotary-slide coupling interconnecting the rotary and displaceable, non-rotary part of the connecting rod linkage.
Controllable pitch propellers for watercraft of varying construction are known in the prior art. When controllable pitch propellers are used in large watercraft, that is for high power ship propulsion systems, adjusting linkages of individual propeller blades are housed in a variable pitch propeller hub. The adjusting linkages are operated by means of a connecting rod which is located in the center of a hollow drive shaft which carries at its end and adjusting flange, on which are supported the adjusting linkages. Reference should be made in this connection to an article in "Internat. Shipbuilding Progress", February/March 71 by J. Wind, "Principles of Mechanisms Used in Controllable Pitch Propellers", particularly FIG. 8. The connecting rod is operated by a hydraulic linear motor comprising cylinders and pistons and is either incorporated into the drive shaft or is connected via an adjusting linkage to the connecting rod, cf., U.S. Pat. No. 3,095,932.
When a correspondingly smaller propulsive output controllable pitch propellers are used in smaller watercraft, adjustment of the propeller blades takes place by means of a mechanical lever bar via a hydraulic linear motor as described in U.S. Pat. No. 4,599,043 or via manual actuation as described in U.S. Pat. No. 2,742,097.
A significant problem which develops in the use of controllable pitch propellers for watercraft is that foreign bodies and in particular barnacles are deposited on the moving parts of the adjusting linkage and these bodies impede or block the adjusting movements of the propeller. This more particularly applies in the case of the connecting rods (the connecting rod linkage) for adjusting the propeller blades wherein as a function of the adjustment position of the blades, parts can temporarily come into contact with the water, see for example, U.S. Pat. No. 4,599,043. FIG. 1 of this patent discloses an adjustable drive for the blades of a controllable pitch propeller whose connecting rods are connected at their free ends to a rotary-slide coupling forming the connection between the rotary and the displaceable, non-rotary part of the connecting rod linkage. The rotary-slide coupling is surrounded by water as are the free ends of the connecting rods located in the rotary propeller hub. It is known to protect by bellows seals or joints, movable parts which have to be protected against environmental influences. However, these arrangements require additional space for installation and are relatively sensitive to damage. Similar conditions also exist with regard to the trimming cylinders of sports boats. Foreign bodies attached to the piston rods can be cleaned by steel stripping rings. However, it is a disadvantage in that this increases the thrust force requirement, without achieving complete cleaning.